Four local mayors plan to participate in a discussion on 95.9FM WATD Monday evening. Braintree Mayor Joseph Sullivan, Brockton Mayor Bill Carpenter, Quincy Mayor Thomas Koch and Weymouth Mayor Sue Kay have also agreed to participate in a roundtable during Monday Night Talk with Kevin Tocci. The segment, which starts at 7 p.m. and will last an hour, will focus on a number of topics each community faces.